Nuclear detectors are used throughout the oil drilling industry for a variety of purposes. In some cases gamma detectors or neutron detectors are lowered into a well to log the formations. In measurement-while-drilling and logging-while-drilling operations, various instruments, including gamma or nuclear detectors, are mounted in a cavity in a drilling tool and used on a real time basis to make critical measurements while the drilling is taking place. In most all of these applications, the space available for installing instruments is very limited. Previous patents have provided for larger detector elements within available space by making more efficient use of the space within gamma detector elements, such as within the scintillation package. However, conventional designs have not fully addressed an important aspect of installing detectors in the drilling tools and mining equipment. Specifically, there is a need to provide shock and vibration isolation for the complete detector assembly and to provide mechanical compliance to the shape of the cavity in the tool, and to do so while using a minimum of space.
Due to the configuration and operational requirements of oil drilling tools, the typical configuration of a nuclear detector and other instrument packages in drilling tools is cylindrical. The cylindrical shape of photo-multiplier tubes, the relative ease of installing circular optical windows, and other considerations often favor a detector being of a cylindrical shape. The trend in recent years has been to reduce the diameter of drilling tools, resulting in less space being available for detectors. The most immediate effect is the necessity to reduce the diameter of the sensor package and associated electronics. In order to retain as much sensitivity of the detector as possible, the length of the scintillation elements are sometimes increased in order to increase the surface and volume available to detect gamma rays. The reduction in space similarly places constraints upon the size of the instrumentation and computer modules associated with the detectors. Therefore, there is a general need to be able to integrate more functions into smaller spaces while maintaining mechanical compliance, thermal compliance, and dynamic suspension.
Best utilization of available space within a drilling tool or mining machine would be achieved by making the nuclear detector assembly, or other instrument package, essentially the same size as the available cavity in the tool or machine. However, such an approach requires that the size and shape of the cavity and the size and shape of the detector be highly controlled. This constraint on the hardware can be expensive and limits interchangeability. Further, differential thermal expansion can damage the hardware unless provisions are made.
The conventional approach has been to use an elastomeric material around the detector assembly, in the shape of boots, pads, or o-rings. In order for an elastomeric material to provide sufficient movement to satisfy the required objectives while also accommodating thermal expansion at the high temperatures, thicker elastomeric materials are needed which use more space. Thicker elastomeric materials tend to lower the resonant frequency of the support assembly thus transmitting high levels of vibration into the instrument. It is desirable in most cases to provide for dynamic isolation but to do so without producing a natural resonant frequency near the frequencies of high levels of induced vibrations or shocks.
A major disadvantage of applying springs in a typical manner is that the springs do not exhibit a high level of damping resulting in high dynamic responses at resonant frequencies. Even elastomers, which have higher damping characteristics than metallic springs, have significant xe2x80x9cQxe2x80x9d values which result in damaging resonant responses when vibrations having a frequency near the resonant frequency enter the detector assembly.
The need for a more space efficient way to provide good dynamic isolation and high levels of damping to allow for enlarged scintillation elements or photomultiplier tubes by making use of flat, or slightly shaped, elongated radial springs has been previously considered. This has proven to be effective inside detector, sensor and electronic assemblies. However, physical constraints and operational considerations make it difficult, if not impossible, in some instances to install such springs around complete gamma detector assemblies or instrument packages.
Oil drilling tools typically provide separate pressure cavities for individual elements of the instrumentation system to protect the instruments from high pressures of up to 25,000 pounds per square inch (psi) or more. The instrumentation elements within these cavities are interconnected with wiring to exchange signals. In some instances, segments of the instrumentation are integrated into modules which are then enclosed in a single pressure cavity. In order to maximize the use of space in the tool, there is a need to integrate more of the electronic elements within a single module. Effective dynamic suspension of the elements within the instrument module and dynamic suspension around such modules can both be important to increasing the reliability of components within.
The invention provides important and substantial solutions to the problems described above.
The invention relates to electro-optical devices and other electronics and instrumentation used in harsh environments to detect and quantify nuclear radiation, such as, for example, oil drilling or solid mineral mining operations. More specifically, the current invention relates to maximizing use of space available for installing a nuclear detection device, or other instrumentation device. A flexible dynamic housing described herein allows a device to be compliant with the geometry and thermal dynamics of the cavity into which it is to be installed, such that the device is effectively isolated from damaging vibrations and shock. Installation is made easier and more reliable. Equipment supported in this manner can be expected to have a longer operational life due to the softer ride that they receive.
The flexible dynamic housing uses metallic springs that have predictable, repeatable mechanical properties. Such springs are much thinner than would be required for elastomers to provide an equivalent amount of dynamic isolation. Further, the springs are not as affected by temperature as are elastomers. As the temperature increases into the range of 150 degrees Celsius to 200 degrees Celsius or more, elastomers expand causing them to be compressed within the contained space in which they are used, resulting in the dynamic properties changing. The properties of the metallic springs employed in the flexible dynamic housing are affected much less by temperature changes and do not degrade, or take a set, with time at temperature.
The typical shape of a nuclear detector assembly or instrumentation package in a drilling tool, and certain other applications, such as, for example, mining applications, is cylindrical. The placement of linear springs along the length of the detector and between the detector and the cavity into which the detector is placed, is an effective way to solve some of the known problems. Such springs provide the desired shock and vibration isolation, provide compliance between small variations in the shape of the detector or the cavity, and provide compliance for changes in geometry due to differential thermal expansion. Another advantage of the flexible dynamic housing is the support is distributed along the length of the package reducing bending and shear forces during high shock and vibration.
These and other advantages and features will be more readily understood from the following detailed description of preferred embodiments of the invention which is provided in connection with the accompanying drawings.